Defending US Open champion Novak Djokovic suffered a shock third-round exit at the hands of Alexei Popyrin.

‍

The 6-4 6-4 2-6 6-4 defeat means the Serb will fail to win a Grand Slam in a single season for the first time since 2017.

‍

Djokovic called his performances at Flushing Meadows this year “some of the worst tennis” he has ever played, hitting 14 double faults and 49 unforced errors in Friday evening's loss.

‍

“He definitely played better and deserved to win today," said Djokovic. "On my end, honestly, the way I felt and the way I played from the beginning of this tournament, third round is a success.

‍

“I mean, I have played some of the worst tennis I've ever played, honestly, serving by far the worst ever.

‍

“Yeah, it was just an awful match for me.”

‍

‍

Having battled hard to win his first Olympic gold medal in Paris this summer, Djokovic conceded that he was feeling the impact throughout the week.

‍

"Obviously it [the Olympics] had an effect,” said Djokovic. “I spent a lot of energy winning the gold, and I arrived to New York just not feeling fresh mentally and physically.

‍

"But because it's the US Open, I gave it a shot and I tried my best. I didn't have any physical issues. I just felt out of gas.

‍

“Yeah, you could argue that it's because of the Olympics, but I don't know. I don't want to analyse that right now.

‍

"Life moves on. I'll try and recalibrate and look for what's next. Tomorrow is a new day."

‍

The 24-time Grand Slam champion crumbled when it mattered most, converting just 25% of his break points, compared with his Australian opponent’s 43%.

‍

‍

And Djokovic’s net game was also found lacking, winning just 19 out of 40 in contrast to Popyrin’s 25 from 36.

‍

“I mean, I tried so many things, and sometimes that's an issue, is that you move away from the basics that work,” explained Djokovic.

‍

“Then you just lose the basics. You lose the foundation. You lose the movement, the timing, the rhythm, the tempo, everything, whether it's a serve or any other shot.

‍

“It was just really a big struggle mentally for me to play these three matches here, because I wasn't playing even close to my best.

‍

“So it's not good to be in that kind of state where you feel okay physically, and of course you're motivated because it's a Grand Slam, but you just are not able to find your game.

‍

“That's it. The game is falling apart, and I guess you have to accept that tournaments like this happen.”

‍

The match marked Popyrin’s first third-round win at a major and his first-ever ATP victory over Djokovic at the fourth attempt.

‍

And the Australian hailed his opponent as the “greatest of all time”, calling his achievement “unbelievable”.

‍

Popyrin said: “It’s unbelievable because I’ve been in the third round about 15 times in my career, but I haven’t been able to get past to the fourth round.

‍

“To be able to do it against the greatest of all time to get into the fourth round is unbelievable. It’s a great feeling and the hard work has paid off.”

‍

And the 37-year-old Serb believes the world No. 28 can go far at this year’s tournament, with a clash against home favourite Frances Tiafoe up next on Sunday.

‍

“If he serves well, plays well, he can beat anybody,” Djokovic said of his opponent.

‍

“Look, Alcaraz is out, I'm out... some big upsets. The draw is opening up. Obviously Sinner is the main favourite, but then Tiafoe is there as well as American favourite, Fritz.

‍

“Zverev, you have great guys playing well, and Rublev, Dimitrov in this part of the draw. Anybody can take it. It's going to be interesting to see who takes the title in the end.”

‍

‍